Changed name of the computer and now it's asking me for the activation code which doesn't work.

I installed Studio 2015 on my PC, but later it was necessary to reinstall the system and we changed the name of the computer. Now SDL thinks I'm trying to install Trados on a different computer. I can't deactivate the old license because the deactivate button won't appear, and Trados keeps asking me for the activation code and when I put it in it says it's already in use. What should I do?